By Thomas on Friday, July 16, 2004 - 04:29 am:

I our laboratory I have a "universal" GC method for determination of solvents in different compounds and formulations. With the method we are able to quantify from methanol (Bp 64) up to NMP with this method. Different solvents are used depending on the specific application, with benzylalkohol as first choice.

I have been asked to do qunatitative analysis on xylenes in a liquid formulation in water. To this application I have used my "universal" GC method, and my headspace sampler. Until now everything look very good, and I got very nice peak for ethyl-benzen, m-xylene and o-xylene.

My problem is (ofcourse) co-eluting of peak corresponding to m-xylene (Bp 139) and p-xylenes (Bp 138).

I am using 624 column, and temperature gradient is as follow; 45°C (5 min hold) to 90°C at 2°C/min then to 220°C at 30°C/min (5min hold)

Is there anyone that have a good method for separating m and p-xylene by GC, then please let me know.

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By chromatographer1 on Friday, July 16, 2004 - 05:47 am:

depending upon the amounts placed on the column, a long 60m 0.32mm or 0.25mm Supelcowax 10 capillary or equivalent will separate the isomers, albeit with a long analysis time. Also the 100ft SCOT DnDP Bentone from Supelco will effectively separate these isomers.

Is it really necessary to separate these isomers?
Why not report the single peak as a unknown mix of the two isomers?

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By Jason Ellis on Friday, July 16, 2004 - 08:28 am:

The analysis time on a wax column won't be too terrible. On the 60m HP-Innowax column m-xylene and p-xylene are eluted in about 12 minutes and are baseline resolved. You can see a chrom here:

http://www.chem.agilent.com/cag/graphics/462c.jpg

Jason Ellis
GC Column Support
Agilent Technologies

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By Thomas on Wednesday, July 21, 2004 - 12:46 am:

I am aware of the possibility to report the peak corresponding to m and p-xylene as mix of the isomeres. According to ICH guidelines for residual solvents, the limit is actually stated as a mixture of m p o-xylene and ethylbenzen, which could be a strong argument for not separating the isomeres.

My question was more a theoretical/technical point.

Thanks you for the respons,
Thomas